NAME¶

std::swap(std::function) - std::swap(std::function)

Synopsis¶

Defined in header <functional>
template< class R, class... Args >
void swap( std::function<R(Args...)>& lhs, std::function<R(Args...)>& (since C++11)
rhs ) noexcept;

Overloads the std::swap algorithm for std::function. Exchanges the state of lhs with
that of rhs. Effectively calls lhs.swap(rhs).

Parameters¶

lhs, rhs - polymorphic function wrappers whose states to swap

Return value¶

(none)

Example¶

// Run this code

#include <functional>
#include <iostream>

void foo(const char* str, int x)
{
std::cout << "foo(\"" << str << "\", " << x << ")\n";
}

void bar(const char* str, int x)
{
std::cout << "bar(\"" << str << "\", " << x << ")\n";
}

int main()
{
std::function<void(const char*, int)> f1{foo};
std::function<void(const char*, int)> f2{bar};

f1("f1", 1);
f2("f2", 2);

std::cout << "std::swap(f1, f2);\n";
std::swap(f1, f2);

f1("f1", 1);
f2("f2", 2);
}

Output:¶

foo("f1", 1)
bar("f2", 2)
std::swap(f1, f2);
bar("f1", 1)
foo("f2", 2)

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2062 C++11 overload of swap for function was not required required
to be noexcept

See also¶

swap swaps the contents
(public member function)
swap(std::move_only_function) overloads the std::swap algorithm
(C++23) (function)